In magnetic disk drives, data is written and read by magnetic transducers called “heads.” The magnetic disks are rotated at high speeds, producing a thin layer of air called an air bearing surface (ABS). The read and write heads are supported over the rotating disk by the ABS, where they either induce or detect flux on the magnetic disk, thereby either writing or reading data. Layered thin film structures are typically used in the manufacture of read and write heads. In write heads, thin film structures provide high areal density, which is the amount of data stored per unit of disk surface area, and in read heads they provide high resolution.
A thin film write head may have two pole pieces, namely, a top pole piece (colloquially referred to as “P2”) and a bottom pole piece (“P1”). A write head generally has two regions, denoted a pole tip region and a back region. The pole pieces are formed from thin magnetic material films and in longitudinal recording heads converge in the pole tip region at a magnetic recording gap, and in the back region at a back gap. In a perpendicular recording write heads, on the other hand, no write gap exists. Instead, the second pole piece P2 is formed with a pole tip that has a width which defines the track width of the write head and a wider yoke portion which delivers the flux to the pole tip. At a recessed end of the pole tip the yoke flares laterally outwardly at a “flare area” to its full width and thence, as in the case of longitudinal recording heads, to a back gap that is magnetically connected to a back gap of a first pole piece.
In any case, a write head thus has at least one pole tip “P2”. The width of the P2 pole at the ABS predominantly defines the write track width of the write head. The height “P2T” of the P2 pole plays a role in determining the amount of flux delivered to the disk, making it an important feature. The write track width, which is related to the width of the bottom of the P2 pole, is especially important because it limits the areal density of a magnetic disk. A narrower track width translates to greater tracks per inch (TPI) written on the disk, which in turn translates to greater areal density.
In the present assignee's co-pending U.S. patent application published as 2005/0023243 and incorporated herein by reference, a process for making a write head is disclosed which includes forming the P2 pole, followed by chemical-mechanical polishing (CMP)-assisted reactive ion (Argon) milling. The reactive ion milling is used for high selectivity to remove only areas desired to be removed for subsequent process steps. As recognized herein, however, portions of the P2 pole undesirably can be removed during the subsequent process steps, requiring that a thicker P2 layer be deposited in the first place to compensate for this removal. As also understood herein, requiring a thicker initial P2 layer means that the as-plated aspect ratio of the P2 layer is relatively high, which is undesirable particularly for P2 poles defined by DUV lithography, because the aspect ratio is limited by the so-called “straight zone” in the trench. Having made these critical observations, the present invention understands that it is desirable to prevent unwanted thinning of certain portions of the P2 pole during post-pole formation steps, to facilitate depositing thinner P2 layers initially.